Film-Tech Forum ARCHIVE: DMA8Plus: any way to automate decode mode switching on Digital Input 1?

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Posted by Antti Nayha (Member # 4980) on 01-16-2013, 06:04 AM:

The title pretty much says it all.

I’m often running DCP’s with 2.0 audio, so I need to keep switching back and forth between Pro Logic decoding and discrete mode on the DMA8Plus for optimal results. It’s a bit of a nuisance, since (AFAIK) you can only do it through the PC application. There's also the considerable risk of forgetting to switch it back to discrete after a 2.0 film – which is disastrous of course, because running a 5.1 film in the Pro Logic mode completely loses the center channel…

I know that it’s easy to automate with the CP750: a Dolby server will automatically show cues that you can program in to switch the decode mode. Not so with the DMA8Plus. Am I missing something?

Posted by Bajsic Bojan (Member # 4928) on 01-16-2013, 06:25 AM:

Why does a 2.0 source material NEED to be decoded via prologic?

I am assuming it is 2.0 for the reason it was mixed as 2.0 and probably intended to be played back at 2.0.

Sorry for not answering your question tho. I can check later if i find a way to do it.

Posted by Antti Nayha (Member # 4980) on 01-16-2013, 07:04 AM:

I would say that a 2.0 discrete (LoRo) mix was never intended to be played back in a cinema environment, period.

If you play any 2.0 track as 2.0 discrete in a cinema, it will sound very unbalanced for most patrons. The most obvious problem is that the dialogue will be seriously off-centre, as the majority of your audience will not be sitting in the dead centre. The wider your seating area is, the worse it gets. You will also lose your subwoofer, which can be a major downside depending on the content.

There are also a lot of 2.0 DCP’s around that have actually been mixed for a surround presentation (LtRt). The problem is that there’s usually no way of knowing: the DCI standard does not allow for flagging the soundtrack as either LoRo or LtRt. And neither the labels on the physical DCP itself nor the accompanying spec sheets usually say anything about this. (There have been a few cases, though, where I was specifically asked to use Pro Logic by the producers or the sound guy.)

I realize that this is a bit controversial, but I think that most 2.0 soundtracks by far will sound much better in a cinema environment when decoded with Pro Logic (or sometimes Pro Logic II). Regardless of whether they were actually mixed in surround or not.

Most 2.0 LoRo tracks decode rather gracefully with Pro Logic, but there are exceptions. Sometimes the 2.0 track has phasing errors, which will result in crazy effects when played back in Pro Logic – such as dialogue coming out of the surrounds. This is rare, though, so my policy is to run all 2.0 content with Pro Logic by default (with a soundcheck first, naturally).

Posted by Richard May (Member # 2627) on 01-16-2013, 08:13 AM:

Sorry to stay off topic but...........

I totally agree that playing 2.0 through decoding sounds better 99% of the time. Why don't they just mix it that way to begin with?

Posted by Bajsic Bojan (Member # 4928) on 01-16-2013, 08:14 AM:

yes, i agree, most probably most dcps didn't start out with the intention of being played back thru 2.0. I also understand the center channel for dialogue statement and i agree.

The thing is, sometimes checking the whole feature or a programme full of shorts is not something that can be done before; sometimes if you check only certain parts of it, it might sound ok there, but then you might loose dialogue in some other scenes you didnt check out; and sometimes you risk the wrath of a director/sound mixer when you run it in prologic. Double edged sword.

But yes, i see your point. Will try it out with certain material when i get the chance. I'm not a real fan of prologic tho, i don't like what it does on most bluray/DVD releases, where the surrounds are just lower leveled L/R. And that i cannot seem to get it work on LtRt material from analogue sources on the cp650.

Posted by Steve Guttag (Member # 268) on 01-16-2013, 08:29 AM:

Is the:

dma8plus.sys.dolby_digital_2_channel_decode_mode

Not working for you? The parameters can be auto, lr_discrete, prologic, prologic_2

The older DMA8 had the command:

4xaes12_input_pl

Which may also work.

Posted by Antti Nayha (Member # 4980) on 01-16-2013, 08:38 AM:

Bajsic: formats 75 and 76 are working fine for me on the CP650…

Steve: thanks, I’ll double-check my commands. Except surely there’s no ”auto” option for Digital Input 1? At least in the GUI there are only three options listed: Pro Logic, Pro Logic II, and Discrete L/R.

Posted by Steve Guttag (Member # 268) on 01-16-2013, 10:39 AM:

Who knows...Dolby's serial command set has always been lacking, in my opinion.

If you use "Expert View" on the DMA8Plus, you can get their command set. It would appear that the commands you want are:

dma8plus.sys.pcm_2_channel_decode_mode_1 lr_discrete

Or

dma8plus.sys.pcm_2_channel_decode_mode_1 prologic.

Posted by Bajsic Bojan (Member # 4928) on 01-16-2013, 11:47 AM:

Well. On the digital1 tab,in the 2channel Dolby decoding box, you can mark the decode to auto or force prologic (i/ii) or discrete.

i tried it now on three 2.0 sources (one mpeg made, one easydcp project, one orca wrapped interop) with forced prologic and it worked on one, it also played 5.1 which was next in list as 5.1 pcm and didnt force prologic. I'll try with the auto setting in 5-6 hours and let you know. i dont know about the other two, not enough time. I'll do more tests later.

Which firmware are you running? And which software version, maybe they are different, as you dont seem to be able to change only the 2channel decoding on digital1 input. I'm running software ver. 1.3.0.

edit: nope, seems it was a glitch and i had 3/2 source. didn't work. and apparently the 2ch decode doesnt matter in case of PCM decoding. :/